Cutting tool

ABSTRACT

A cutting tool includes: a substrate including a rake face; and a coating film that coats the rake face, wherein the coating film includes an α-Al2O3 layer disposed on the substrate, the α-Al2O3 layer includes crystal grains of α-Al2O3, an area ratio of crystal grains oriented in (001) among the crystal grains is 50% to 90% in the α-Al2O3 layer at the rake face, and a film residual stress AA determined based on a crystal plane interval of a (001) plane of the α-Al2O3 layer at the rake face is more than 0 MPa and less than or equal to 2000 MPa, and a film residual stress BA determined based on a crystal plane interval of a (110) plane of the α-Al2O3 layer at the rake face is more than or equal to −1000 MPa and less than 0 MPa.

TECHNICAL FIELD

The present disclosure relates to a cutting tool. The presentapplication claims a priority based on Japanese Patent Application No.2018-194134 filed on Oct. 15, 2018, the entire content of which isincorporated herein by reference.

BACKGROUND ART

Conventionally, a cutting tool having a substrate coated with a coatingfilm has been used. For example, Japanese Patent Laying-Open No.2004-284003 (Patent Literature 1) discloses a surface-coated cuttingtool having a coating film including an α-Al₂O₃ layer in which a totalarea of crystal grains exhibiting a crystal orientation of a (0001)plane is more than or equal to 70% when seen in a plan view in thenormal direction of a surface of the layer.

Moreover, Japanese Patent Laying-Open No. 2009-028894 (Patent Literature2) discloses a coated cutting tool having a cemented carbide body and acoating, wherein at least an outermost layer of the coating is anα-Al₂O₃ layer that has a thickness of 7 to 12 μm and that is oriented ina (006) direction, an orientation coefficient TC (006) thereof is morethan 2 and less than 6, each of orientation coefficients TC (012), TC(110), TC (113), TC (202), TC (024) and TC (116) is less than 1, and anorientation coefficient TC (104) is the second largest orientationcoefficient.

CITATION LIST Patent Literature

PTL 1: Japanese Patent Laying-Open No. 2004-284003

PTL 2: Japanese Patent Laying-Open No. 2009-028894

SUMMARY OF INVENTION

A cutting tool according to the present disclosure is a cutting toolincluding: a substrate including a rake face; and a coating film thatcoats the rake face, wherein

the coating film includes an α-Al₂O₃ layer disposed on the substrate,

the α-Al₂O₃ layer includes crystal grains of α-Al₂O₃,

an area ratio of crystal grains oriented in (001) among the crystalgrains is more than or equal to 50% and less than or equal to 90% in theα-Al₂O₃ layer at the rake face, and

in a residual stress measurement performed in accordance with a 2θ-sin²ψmethod using X rays,

-   -   a film residual stress A_(A) determined based on a crystal plane        interval of a (001) plane of the α-Al₂O₃ layer at the rake face        is more than 0 MPa and less than or equal to 2000 MPa, and    -   a film residual stress B_(A) determined based on a crystal plane        interval of a (110) plane of the α-Al₂O₃ layer at the rake face        is more than or equal to −1000 MPa and less than 0 MPa.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view illustrating one embodiment of a substrateof a cutting tool.

FIG. 2 shows an exemplary color map in a processed surface of an α-Al₂O₃layer.

FIG. 3 is a schematic cross sectional view showing a region in athickness direction of the α-Al₂O₃ layer.

FIG. 4 is a graph schematically showing a stress distribution in thethickness direction of the α-Al₂O₃ layer.

FIG. 5 is a schematic cross sectional view showing an exemplary chemicalvapor deposition apparatus used to manufacture a coating film.

FIG. 6 is a schematic cross sectional view of the cutting tool accordingto the present embodiment.

DETAILED DESCRIPTION Problem to be Solved by the Present Disclosure

In each of Patent Literature 1 and Patent Literature 2, since thecoating film having the α-Al₂O₃ layer configured as described above isincluded, mechanical characteristics of the surface-coated cutting tool,such as wear resistance (for example, crater wear resistance or thelike) and breakage resistance, are improved, with the result that thelife of the cutting tool is expected to be long.

However, in recent years, cutting has been performed at a higher speedwith higher efficiency. This leads to an increased load imposed on acutting tool, with the result that the life of the cutting tool tends tobe short. Accordingly, it has been required to further improvemechanical characteristics of a coating film of a cutting tool.

The present disclosure has been made in view of the above-describedcircumstances, and has an object to provide a cutting tool excellent inchipping resistance and crater wear resistance.

Advantageous Effect of the Present Disclosure

According to the present disclosure, a cutting tool excellent inchipping resistance and crater wear resistance can be provided.

DESCRIPTION OF EMBODIMENTS

First, embodiments of the present disclosure are listed and described.

[1] A cutting tool according to the present disclosure is a cutting toolincluding: a substrate including a rake face; and a coating film thatcoats the rake face, wherein

the coating film includes an α-Al₂O₃ layer disposed on the substrate,

the α-Al₂O₃ layer includes crystal grains of α-Al₂O₃,

an area ratio of crystal grains oriented in (001) among the crystalgrains is more than or equal to 50% and less than or equal to 90% in theα-Al₂O₃ layer at the rake face, and

in a residual stress measurement performed in accordance with a 2θ-sin²ψmethod using X rays,

-   -   a film residual stress A_(A) determined based on a crystal plane        interval of a (001) plane of the α-Al₂O₃ layer at the rake face        is more than 0 MPa and less than or equal to 2000 MPa, and    -   a film residual stress B_(A) determined based on a crystal plane        interval of a (110) plane of the α-Al₂O₃ layer at the rake face        is more than or equal to −1000 MPa and less than 0 MPa.

Since the cutting tool is configured as described above, the cuttingtool can have an excellent chipping resistance and an excellent craterwear resistance. Here, the term “chipping resistance” refers to acharacteristic of suppressing breakage or detachment of only a surfacelayer of the coating film.

[2] The α-Al₂O₃ layer has a thickness of more than or equal to 1 μm andless than or equal to 20 μm,

in a residual stress measurement performed in accordance with a constantpenetration depth method using X rays at a region r1 interposed betweena virtual plane D1 and a virtual plane D2, the virtual plane D1 beinglocated at a distance d₁₀ from a surface of the α-Al₂O₃ layer oppositeto the substrate toward the substrate side, the distance d₁₀ being 10%of the thickness of the α-Al₂O₃ layer, the virtual plane D2 beinglocated at a distance d₄₀ from the surface of the α-Al₂O₃ layer oppositeto the substrate toward the substrate side, the distance d₄₀ being 40%of the thickness of the α-Al₂O₃ layer,

-   -   a residual stress A determined based on the crystal plane        interval of the (001) plane of the α-Al₂O₃ layer at the rake        face is more than or equal to −200 MPa and less than or equal to        2000 MPa, and    -   a residual stress B determined based on the crystal plane        interval of the (110) plane of the α-Al₂O₃ layer at the rake        face is more than or equal to −1500 MPa and less than or equal        to 700 MPa, and

a relational expression of A>B is satisfied. By defining in this way, acutting tool more excellent in chipping resistance can be provided.

[3] A stress distribution of the residual stress A has

-   -   a first a region in which the residual stress A is decreased        continuously from the surface of the α-Al₂O₃ layer opposite to        the substrate toward the substrate side, and    -   a second a region which is located at the substrate side        relative to the first a region and in which the residual stress        A is increased continuously from the surface opposite to the        substrate toward the substrate side, and

the first a region and the second a region are continuous to each othervia a minimum point of the residual stress A. By defining in this way, acutting tool more excellent in crater wear resistance can be provided.

[4] A stress distribution of the residual stress B has

-   -   a first b region in which the residual stress B is decreased        continuously from the surface of the α-Al₂O₃ layer opposite to        the substrate toward the substrate side, and    -   a second b region which is located at the substrate side        relative to the first b region and in which the residual stress        B is increased continuously from the surface opposite to the        substrate toward the substrate side, and

the first b region and the second b region are continuous to each othervia a minimum point of the residual stress B. By defining in this way, acutting tool more excellent in crater wear resistance can be provided.

[5] The coating film further includes one or more intermediate layersdisposed between the substrate and the α-Al₂O₃ layer, and

each of the intermediate layers includes a compound that is composed ofat least one element selected from a group consisting of a group 4element, a group 5 element, a group 6 element in a periodic table, Aland Si, and at least one element selected from a group consisting of C,N, B, and O. By defining in this way, a cutting tool more excellent inchipping resistance and crater wear resistance can be provided.

DETAILS OF EMBODIMENTS OF THE PRESENT DISCLOSURE

The following describes one embodiment (hereinafter, referred to as “thepresent embodiment”) of the present disclosure. However, the presentembodiment is not limited thereto. In the present specification, theexpression “X to Y” represents a range of lower to upper limits (i.e.,more than or equal to X and less than or equal to Y). When no unit isindicated for X and a unit is indicated only for Y, the unit of X is thesame as the unit of Y. Further, in the present specification, when acompound is expressed by a chemical formula in which a composition ratioof composition elements is not limited such as “TiC”, it is assumed thatthe chemical formula includes all the conventionally known compositionratios (element ratios). In this case, it is assumed that theabove-described chemical formula includes not only a stoichiometriccomposition but also a non-stoichiometric composition. For example, thechemical formula “TiC” includes not only a stoichiometric composition“Ti₁C₁” but also a non-stoichiometric composition such as “Ti₁C_(0.8)”.The same also applies to compounds other than the “TiC”.

<<Cutting Tool>>

A cutting tool according to the present disclosure is a cutting toolincluding: a substrate including a rake face; and a coating film thatcoats the rake face, wherein

the coating film includes an α-Al₂O₃ layer disposed on the substrate,

the α-Al₂O₃ layer includes crystal grains of α-Al₂O₃,

an area ratio of crystal grains oriented in (001) among the crystalgrains is more than or equal to 50% and less than or equal to 90% in theα-Al₂O₃ layer at the rake face, and

in a residual stress measurement performed in accordance with a 2θ-sin²ψmethod using X rays,

-   -   a film residual stress A_(A) determined based on a crystal plane        interval of a (001) plane of the α-Al₂O₃ layer at the rake face        is more than 0 MPa and less than or equal to 2000 MPa, and    -   a film residual stress B_(A) determined based on a crystal plane        interval of a (110) plane of the α-Al₂O₃ layer at the rake face        is more than or equal to −1000 MPa and less than 0 MPa.

The surface-coated cutting tool (hereinafter, also simply referred to as“cutting tool”) of the present embodiment includes the substrate havingthe rake face, and the coating film that coats the rake face. In anotheraspect of the present embodiment, the coating film may coat a portion(for example, a flank face) of the substrate other than the rake face.Examples of the above-described cutting tool include a drill, an endmill, an indexable cutting insert for drill, an indexable cutting insertfor end mill, an indexable cutting insert for milling, an indexablecutting insert for turning, a metal saw, a gear cutting tool, a reamer,a tap, and the like.

<Substrate>

For the substrate of the present embodiment, any conventionally knownsubstrate for such a purpose of use can be used. For example, thesubstrate preferably includes at least one selected from a groupconsisting of: a cemented carbide (for example, a tungsten carbide (WC)based cemented carbide, a cemented carbide including Co in addition toWC, or a cemented carbide having a carbonitride of Cr, Ti, Ta, Nb, orthe like added therein in addition to WC); a cermet (including TiC, TiN,TiCN, or the like as a main component); a high-speed steel; a ceramic(titanium carbide, silicon carbide, silicon nitride, aluminum nitride,aluminum oxide, or the like); a cubic boron nitride sintered material(cBN sintered material); and a diamond sintered material. The substratemore preferably includes at least one selected from a group consistingof the cemented carbide, the cermet, and the cBN sintered material.

Among these various substrates, it is particularly preferable to selectthe WC based cemented carbide or the cBN sintered material. This is dueto the following reason: each of these substrates is excellent inbalance between hardness and strength particularly at a hightemperature, and has an excellent characteristic as a substrate of acutting tool for the above-described purpose of use.

When the cemented carbide is used as the substrate, the effects of thepresent embodiment are achieved even if the cemented carbide includesfree carbon or an abnormal phase called phase in the structure thereof.It should be noted that the substrate used in the present embodiment mayhave a modified surface. For example, in the case of the cementedcarbide, a β-free layer may be formed on the surface. In the case of thecBN sintered material, a surface hardening layer may be formed. Evenwhen the surface is thus modified, the effects of the present embodimentare exhibited.

FIG. 1 is a perspective view illustrating one embodiment of thesubstrate of the cutting tool. The substrate having such a shape is usedas a substrate of an indexable cutting insert for turning, for example.Substrate 10 has a rake face 1, a flank face 2, and a cutting edgeridgeline portion 3 at which rake face 1 and flank face 2 cross eachother. That is, rake face 1 and flank face 2 are surfaces connected toeach other with cutting edge ridgeline portion 3 being interposedtherebetween. Cutting edge ridgeline portion 3 constitutes a cuttingedge tip portion of substrate 10. The shape of such a substrate 10 canalso be regarded as the shape of the above-described cutting tool.

When the cutting tool is an indexable cutting insert, a substrate 10having a chip breaker or a substrate 10 having no chip breaker may beincluded. The shape of cutting edge ridgeline portion 3 includes any ofa sharp edge (a ridge where the rake face and the flank face cross eachother), a honed edge (a sharp edge processed to be rounded), a negativeland (beveled), and a combination of the honed edge and the negativeland.

In the description above, the shape of substrate 10 and the respectivenames of the portions thereof have been described with reference toFIG. 1. The same terms as those described above will be used for shapeand names of portions corresponding to substrate 10 in the cutting toolaccording to the present embodiment. That is, cutting tool 50 describedabove has rake face 1, flank face 2, and cutting edge ridgeline portion3 that connects rake face 1 and flank face 2 to each other (see FIG. 6).

<Coating Film>

A coating film 40 according to the present embodiment includes anα-Al₂O₃ layer 20 provided on substrate 10 (see FIG. 6). The “coatingfilm” has a function of improving various characteristics in the cuttingtool such as chipping resistance and wear resistance by coating at leasta portion (for example, a portion to be brought into contact with aworkpiece during cutting) of the rake face. The coating film is notlimited to coat a portion of the rake face, and preferably coats theentire surface of the rake face. The coating film may coat the entiresurface of the substrate. However, a coating film that does not coat aportion of the rake face and a coating film having a partially differentconfiguration are not deviated from the scope of the present embodiment.

The thickness of the coating film is preferably more than or equal to 3μm and less than or equal to 50 μm, and is more preferably more than orequal to 5 μm and less than or equal to 25 μm. Here, the thickness ofthe coating film refers to a total of respective thicknesses of layersincluded in the coating film. Examples of the “layers included in thecoating film” include an α-Al₂O₃ layer, an intermediate layer, anunderlying layer, an outermost layer, and the like, which are describedbelow. The thickness of the coating film can be determined, for example,as follows: a scanning transmission electron microscope (STEM) is usedto measure thicknesses at ten arbitrary points in a cross sectionalsample parallel to the normal direction of the surface of the substrate,and the average value of the measured thicknesses at the ten points isdetermined. The same applies to respective measurements of thicknessesof the α-Al₂O₃ layer, the intermediate layer, the underlying layer, andthe outermost layer, which are described below. Examples of the scanningtransmission electron microscope include JEM-2100F (trademark) providedby JEOL.

(α-Al₂O₃ Layer)

The α-Al₂O₃ layer of the present embodiment includes crystal grains ofα-Al₂O₃ (aluminum oxide having an α type crystal structure)(hereinafter, also simply referred to as “crystal grains”). That is, theα-Al₂O₃ layer is a layer including polycrystal α-Al₂O₃.

The α-Al₂O₃ layer may be provided directly on the substrate or may beprovided on the substrate with another layer such as the below-describedintermediate layer being interposed therebetween as long as the effectsexhibited by the cutting tool according to the present embodiment arenot compromised. On the α-Al₂O₃ layer, another layer such as anoutermost layer may be provided. Moreover, the α-Al₂O₃ layer may be theoutermost layer (outermost surface layer) of the coating film.

The α-Al₂O₃ layer has the following features. That is, an area ratio ofcrystal grains oriented in (001) among the crystal grains is more thanor equal to 50% and less than or equal to 90% in the α-Al₂O₃ layer atthe rake face. In another aspect of the present embodiment, an arearatio of crystal grains other than the crystal grains oriented in (001)is more than or equal to 10% and less than or equal to 50% at the rakeface. Moreover, a total of the area ratio of the crystal grains orientedin (001) and the area ratio of the crystal grains other than the crystalgrains oriented in (001) is 100%.

In still another aspect of the present embodiment, when a color map isprepared based on respective crystal orientations of the crystal grainsspecified from an electron backscatter diffraction image analysisperformed using a field emission type scanning electron microscope ontoa mirror-polished, processed surface of the α-Al₂O₃ layer, the arearatio of the crystal grains oriented in (001) may be more than or equalto 50% and less than or equal to 90% in the color map. The processedsurface of the α-Al₂O₃ layer is parallel to the surface of the substrateat the rake face.

Since the area ratio of the crystal grains of α-Al₂O₃ oriented in (001)in the α-Al₂O₃ layer at the rake face is more than or equal to 50% andless than or equal to 90%, the α-Al₂O₃ layer has a particularorientation ((001) orientation), whereby the cutting tool of the presentembodiment can sufficiently obtain an effect of improving the strengthof the coating film. Moreover, when the coating film coats the entiresurface of the substrate, an area ratio of crystal grains oriented in(001) in the α-Al₂O₃ layer at a surface of the substrate other than therake face may be more than or equal to 50% and less than or equal to 90%or may have a value falling out of the range of more than or equal to50% and less than or equal to 90% in the cutting tool of the presentembodiment.

Here, the “crystal grains of α-Al₂O₃ oriented in (001)” or the “crystalgrains oriented in (001)” refer to crystal grains of α-Al₂O₃ in each ofwhich an inclination angle of the (001) plane (an angle formed betweenthe normal line of a surface (facing the coating film) of the substrateand the normal line of the (001) plane) is 0 to 20° relative to thenormal line of the surface of the substrate. Whether or not arbitrarycrystal grains of α-Al₂O₃ are oriented in (001) in the α-Al₂O₃ crystallayer can be confirmed using a field emission type scanning electronmicroscope (FE-SEM) including an electron backscatter diffractionapparatus (EBSD apparatus). The electron backscatter diffraction imageanalysis (EBSD image analysis) is an analysis method based on automaticanalysis of a Kikuchi diffraction pattern generated by backscatteredelectrons. In addition, the “crystal grains other than the crystalgrains of α-Al₂O₃ oriented in (001)” or the “crystal grains other thanthe crystal grains oriented in (001)” refer to crystal grains of α-Al₂O₃in each of which the inclination angle of the (001) plane is more than20° relative to the normal line of the surface of the substrate.

For example, an FE-SEM including an EBSD apparatus is used to capture animage of the mirror-polished, processed surface of the α-Al₂O₃ layerparallel to the surface of the substrate at the rake face. Next, anangle is calculated which is formed between the normal direction of the(001) plane of each pixel of the captured image and the normal directionof the surface of the substrate (i.e., the linear direction of theprocessed surface parallel to the thickness direction of the α-Al₂O₃layer). Then, pixels in each of which the angle is 0 to 20° areselected. Each of the selected pixels corresponds to a crystal grain ofα-Al₂O₃ in which the inclination angle of the (001) plane is 0 to 20°relative to the surface of the substrate, i.e., corresponds to the“crystal grain of α-Al₂O₃ oriented in (001)”.

The area ratio of the crystal grains of α-Al₂O₃ oriented in (001) at apredetermined region (i.e., a color map) of the processed surface of theα-Al₂O₃ layer is calculated based on the color map prepared by providingcolors to the selected pixels for the purpose of classification for theprocessed surface of the α-Al₂O₃ layer as crystal orientation mapping.In the crystal orientation mapping, predetermined colors are provided tothe selected pixels. Hence, the area ratio of the crystal grains ofα-Al₂O₃ oriented in (001) at the predetermined region can be calculatedusing the provided colors as indices. The calculation of the formedangle, the selection of the pixels in each of which the angle is 0 to20°, and the calculation of the area ratio can be performed usingcommercially available software (trademark: “Orientation ImagingMicroscopy Ver 6.2” provided by EDAX), for example.

FIG. 2 shows an exemplary color map for the above-described processedsurface of α-Al₂O₃ layer 20. In FIG. 2, crystal grains 21 oriented in(001) are represented by regions that are surrounded by solid lines andthat are indicated by left oblique hatchings, and crystal grains 22other than the crystal grains oriented in (001) are represented byregions that are surrounded by solid lines and that are indicated by awhite color. That is, in the color map illustrated in FIG. 2, the leftoblique hatchings represent the crystal grains in each of which theangle of the normal direction of the (001) plane relative to the normaldirection of the surface of α-Al₂O₃ layer 20 is 0 to 20°. Moreover, thewhite color represents the crystal grains in each of which the angle ofthe normal direction of the (001) plane relative to the normal directionof the surface of α-Al₂O₃ layer 20 is more than 20°.

From the crystal orientation mapping (color map), in the presentembodiment, it is specified that the processed surface of the α-Al₂O₃layer includes a portion in which the area ratio of the crystal grainsof α-Al₂O₃ oriented in (001) is more than or equal to 50% and less thanor equal to 90%. The area ratio of the crystal grains of α-Al₂O₃oriented in (001) is preferably more than or equal to 50% and less thanor equal to 90%, and is more preferably more than or equal to 55% andless than or equal to 85%.

It should be noted that for the calculation of the area ratio of thecrystal grains of α-Al₂O₃ oriented in (001), an observationmagnification of the FE-SEM is set to 5000×. Moreover, an observed areais set to 450 μm² (30 μm×15 μm). The number of measurement fields is setto more than or equal to 3.

The thickness of the α-Al₂O₃ layer is preferably more than or equal to 1μm and less than or equal to 20 μm, and is more preferably more than orequal to 4 μm and less than or equal to 15 μm.

(Residual Stress of α-Al₂O₃ Layer)

(Film Residual Stress by 2θ-sin²ψ Method)

In the α-Al₂O₃ layer in the present embodiment, in a residual stressmeasurement performed in accordance with a 2θ-sin²ψ method using X rays,

-   -   a film residual stress A_(A) determined based on a crystal plane        interval of a (001) plane of the α-Al₂O₃ layer at the rake face        is more than 0 MPa and less than or equal to 2000 MPa, and    -   a film residual stress B_(A) determined based on a crystal plane        interval of a (110) plane of the α-Al₂O₃ layer at the rake face        is more than or equal to −1000 MPa and less than 0 MPa.

Here, the “residual stress” refers to one type of internal stress(inherent strain) in a layer. The residual stress is divided roughlyinto a compressive residual stress and a tensile residual stress. Thecompressive residual stress refers to a residual stress represented by anumerical value with a negative sign “−” (minus) (indicated by “MPa” asa unit in the present specification). For example, it can be understoodthat a “compressive residual stress of 100 MPa” is a residual stress of−100 MPa. Hence, a concept “large compressive residual stress” indicatesthat the absolute value of the above-described numerical value is large,and a concept “small compressive residual stress” indicates that theabsolute value of the above-described numerical value is small.

The tensile residual stress refers to a residual stress represented by anumerical value with a positive sign “+” (plus) (indicated by “MPa” as aunit in the present specification). For example, it can be understoodthat a “tensile residual stress of 100 MPa” is a residual stress of 100MPa. Hence, a concept “large tensile residual stress” indicates that theabove-described numerical value is large, and a concept “small tensileresidual stress” indicates that the numerical value is small.

In the present embodiment, the expression “film residual stress A_(A)determined based on the crystal plane interval of the (001) plane at therake face” refers to a residual stress that reflects a whole of apredetermined measurement visual field at the rake face and that iscalculated based on the crystal plane interval of the (001) plane in thewhole of the predetermined measurement visual field. Film residualstress A_(A) is calculated by the residual stress measurement performedin accordance with the 2θ-sin²ψ method using X rays. A specific methodthereof is as follows. First, for the whole of the measurement visualfield, the crystal plane interval of the (001) plane is measured inaccordance with the 2θ-sin²ψ method. Here, for an angle of diffractionduring the measurement, an angle of diffraction corresponding to acrystal plane to be measured is designated. The measurement visual fielddescribed above refers to a “measurement visual field at the surface ofthe α-Al₂O₃ layer”. Next, based on the measured crystal plane intervalof the (001) plane, the residual stress of the whole of the measurementvisual field is calculated. Such measurement is performed at a pluralityof measurement visual fields, and the average value of respectiveresidual stresses calculated in the measurement visual fields isregarded as “film residual stress A_(A)”.

When the area ratio of the crystal grains oriented in (001) is more thanor equal to 50%, it is considered that residual stresses included in thecrystal grains oriented in (001) greatly contribute to film residualstress A_(A). Due to such a reason, the present inventors consider thatfilm residual stress A_(A) can be regarded as the residual stressesincluded in the crystal grains oriented in (001).

In the present embodiment, the residual stress is measured in accordancewith the 2θ-sin²ψ method under the following conditions.

Apparatus: SmartLab (provided by Rigaku)

X-ray: Cu/Kα/45 kV/200 mA

Counter: D/teX Ultra250 (provided by Rigaku)

Scanning range: 89.9° to 91.4° (inclination method) in the case of filmresidual stress A_(A)

-   -   37.0° to 38.4° (inclination method) in the case of film residual        stress B_(A)

In the present embodiment, the expression “film residual stress B_(A)determined based on the crystal plane interval of the (110) plane at therake face” refers to a residual stress that reflects a whole of apredetermined measurement visual field at the rake face and that iscalculated based on the crystal plane interval of the (110) plane in thewhole of the predetermined measurement visual field. Film residualstress B_(A) is calculated by the residual stress measurement performedin accordance with the 2θ-sin²ψ method using X rays. A specific methodthereof is as follows. First, for the whole of the measurement visualfield, the crystal plane interval of the (110) plane is measured inaccordance with the 2θ-sin²ψ method. Here, the measurement visual fielddescribed above refers to a “measurement visual field at the surface ofthe α-Al₂O₃ layer”. Next, based on the measured crystal plane intervalof the (110) plane, the residual stress of the whole of the measurementvisual field is calculated. Such measurement is performed at a pluralityof measurement visual fields, and the average value of respectiveresidual stresses calculated in the measurement visual fields isregarded as “film residual stress B_(A)”.

Film residual stress B_(A) tends to exhibit a higher compressiveresidual stress value than that of film residual stress A_(A). Due tosuch a reason, the present inventors consider that the residual stressesincluded in the crystal grains other than the crystal grains oriented in(001) greatly contribute to film residual stress B_(A) as compared withfilm residual stress A_(A).

(Residual Stress of α-Al₂O₃ Layer in Depth Direction)

(Residual Stress by Constant Penetration Depth Method)

Preferably, in the present embodiment, in a residual stress measurementperformed in accordance with a constant penetration depth method using Xrays at a region r1 interposed between a virtual plane D1 and a virtualplane D2, the virtual plane D1 being located at a distance d₁₀ from asurface of the α-Al₂O₃ layer opposite to the substrate toward thesubstrate side, the distance d₁₀ being 10% of the thickness of theα-Al₂O₃ layer, the virtual plane D2 being located at a distance d₄₀ fromthe surface of the α-Al₂O₃ layer opposite to the substrate toward thesubstrate side, the distance d₄₀ being 40% of the thickness of theα-Al₂O₃ layer,

-   -   a residual stress A determined based on the crystal plane        interval of the (001) plane of the α-Al₂O₃ layer at the rake        face is more than or equal to −200 MPa and less than or equal to        2000 MPa, and    -   a residual stress B determined based on the crystal plane        interval of the (110) plane of the α-Al₂O₃ layer at the rake        face is more than or equal to −1500 MPa and less than or equal        to 700 MPa, and

a relational expression of A>B is satisfied (for example, FIG. 3).

Preferably, in another aspect of the present embodiment, the α-Al₂O₃layer has a thickness of more than or equal to 1 μm and less than orequal to 20 μm,

in a residual stress measurement performed in accordance with a constantpenetration depth method using X rays at a region r1 interposed betweena virtual plane D1 and a virtual plane D2, the virtual plane D1 beinglocated at a distance d₁₀ from a surface of the α-Al₂O₃ layer oppositeto the substrate toward the substrate side, the distance d₁₀ being 10%of the thickness of the α-Al₂O₃ layer, the virtual plane D2 beinglocated at a distance d₄₀ from the surface of the α-Al₂O₃ layer oppositeto the substrate toward the substrate side, the distance d₄₀ being 40%of the thickness of the α-Al₂O₃ layer,

-   -   a residual stress A determined based on the crystal plane        interval of the (001) plane of the α-Al₂O₃ layer at the rake        face is more than or equal to −200 MPa and less than or equal to        2000 MPa, and    -   a residual stress B determined based on the crystal plane        interval of the (110) plane of the α-Al₂O₃ layer at the rake        face is more than or equal to −1500 MPa and less than or equal        to 700 MPa, and

a relational expression of A>B is satisfied.

In the present embodiment, the expression “residual stress A determinedbased on the crystal plane interval of the (001) plane at the rake face”refers to a residual stress at a predetermined depth location of therake face, the residual stress being calculated based on the crystalplane interval of the (001) plane. Residual stress A is calculated inaccordance with the constant penetration depth method using X rays. Aspecific method thereof is as follows. First, for the whole of themeasurement visual field, the crystal plane interval of the (001) planeat the predetermined depth location is measured in accordance with theconstant penetration depth method. Here, the measurement visual fieldrefers to a “measurement visual field at a virtual plane that isparallel to the surface of the α-Al₂O₃ layer and that passes through thepredetermined depth location”. Next, based on the measured crystal planeinterval of the (001) plane, the residual stress of the whole of themeasurement visual field is calculated. Such measurement is performed ata plurality of measurement visual fields, and the average value ofrespective residual stresses calculated in the measurement visual fieldsis regarded as “residual stress A”.

In the present embodiment, the residual stress is measured in accordancewith the constant penetration depth method under the followingconditions.

Apparatus: Spring-8 BL16XU

X-ray energy: 10 keV (λ=0.124 nm)

X-ray beam diameter: 0.4 to 1.8 mm (changed depending on a penetrationdepth)

Used diffraction plane: (001) plane in the case of residual stress A

-   -   (110) plane in the case of residual stress B

In the present embodiment, the expression “residual stress B determinedbased on the crystal plane interval of the (110) plane at the rake face”refers to a residual stress at a predetermined depth location of therake face, the residual stress being calculated based on the crystalplane interval of the (110) plane. Residual stress B is calculated inaccordance with the constant penetration depth method using X rays.

Whether or not residual stress A and residual stress B are residualstresses falling within respective predetermined numerical ranges atregion r1 can be determined by measuring, in accordance with theconstant penetration depth method using the X rays, residual stresses A(A_(d10) and A_(d40)) and B (B_(d10) and B_(d40))) at the depth locationof predetermined distance d₁₀ and the depth location of predetermineddistance do in the α-Al₂O₃ layer. Specifically, (1) first, residualstress A_(d10) and residual stress B_(d10) at a certain measurementvisual field on virtual plane D1 are measured in accordance with theconstant penetration depth method. (2) Next, the constant penetrationdepth method is also employed to measure residual stress A_(d40) andresidual stress B_(d40) at a visual field located on virtual plane D2just below the certain measurement visual field on the virtual plane D1within the same region as the region in which the certain measurementvisual field is located. (3) When measured residual stresses A_(d10) andA_(d40) and residual stresses B_(d10) and B_(d40) fall within theabove-described respective numerical ranges and A_(d10)>B_(d10) andA_(d40)>B_(d40) are satisfied, it is determined that “residual stress Aand residual stress B fall within the respective numerical ranges atregion r1 and the relational expression of A>B is satisfied”.

(Residual Stress Distribution of α-Al₂O₃ Layer)

Preferably, in α-Al₂O₃ layer 20 according to the present embodiment, astress distribution of the residual stress A has

-   -   a first a region in which the residual stress A is decreased        continuously from the surface of the α-Al₂O₃ layer opposite to        the substrate toward the substrate side, and    -   a second a region which is located at the substrate side        relative to the first a region and in which the residual stress        A is increased continuously from the surface opposite to the        substrate toward the substrate side, and

the first a region and the second a region are continuous to each othervia a minimum point of the residual stress A.

An exemplary stress distribution is shown in FIG. 4. In the graph ofFIG. 4, the vertical axis represents a residual stress and thehorizontal axis represents a location in the thickness direction ofα-Al₂O₃ layer 20. For the vertical axis, a negative value indicates thatthere is a compressive residual stress in α-Al₂O₃ layer 20, a positivevalue indicates that there is a tensile residual stress in α-Al₂O₃ layer20, and a value of 0 indicates that there is no stress in α-Al₂O₃ layer20.

With reference to FIG. 4, for example, the stress distribution (curve aof FIG. 4) of residual stress A in the thickness direction of α-Al₂O₃layer 20 includes: a first a region P1 a in which the value of theresidual stress is decreased continuously from the upper surface side(the surface side or the surface side opposite to the substrate) towardthe lower surface side (the substrate side); and a second a region P2 awhich is located at the lower surface side relative to the first aregion and in which the value of the residual stress is increasedcontinuously from the upper surface side toward the lower surface side.Here, the second a region has a point at which the residual stress ischanged from the compressive residual stress to the tensile residualstress. The first a region and the second a region are preferablycontinuous to each other via a minimum point P3 a at which the value ofthe residual stress becomes minimum. This minimum point P3 a is locatedat a location close to the upper surface relative to the lower surface.

Since α-Al₂O₃ layer 20 has the above-described stress distribution, abalance between the crater wear resistance and chipping resistance ofα-Al₂O₃ layer 20 becomes more excellent in intermittent cutting. This isdue to the following reason: an impact applied to α-Al₂O₃ layer 20 fromthe upper surface side of α-Al₂O₃ layer 20 is absorbed sufficientlybetween the upper surface side and minimum point P3 a, and a high crackprogression resistance is exhibited at the lower surface side relativeto minimum point P3 a.

In the stress distribution of residual stress A, the value of theresidual stress is preferably more than or equal to −1000 MPa and lessthan or equal to 2000 MPa. In other words, in the stress distribution ofresidual stress A, the absolute value of the compressive residual stressis preferably less than or equal to 1000 MPa (i.e., more than or equalto −1000 MPa and less than 0 MPa), and the absolute value of the tensileresidual stress is preferably less than or equal to 2000 MPa (i.e., morethan 0 MPa and less than or equal to 2000 MPa). In this case, both thechipping resistance and the crater wear resistance tend to be exhibitedappropriately.

Moreover, minimum point P3 a is preferably positioned to have a distanceof 0.1 to 40% of the thickness of the α-Al₂O₃ layer 20 from the surface(upper surface) opposite to the substrate. In this case, a damage formof α-Al₂O₃ layer 20 becomes stable to suppress, for example, suddenchipping of the coating film, whereby variation in the life of the toolcan be reduced. For example, when the thickness of α-Al₂O₃ layer 20 is 1to 20 μm, the location of minimum point P3 a is preferably 0.1 to 8 μmfrom the surface opposite to the substrate. Moreover, the value of theresidual stress at minimum point P3 a is preferably −300 to 900 MPa, ismore preferably −200 to 850 MPa, and is further preferably −100 to 750MPa.

Preferably, in the present embodiment, a stress distribution of theresidual stress B has

-   -   a first b region in which the residual stress B is decreased        continuously from the surface of the α-Al₂O₃ layer opposite to        the substrate toward the substrate side, and    -   a second b region which is located at the substrate side        relative to the first b region and in which the residual stress        B is increased continuously from the surface opposite to the        substrate toward the substrate side, and

the first b region and the second b region are continuous to each othervia a minimum point of the residual stress B.

In the stress distribution (curve b of FIG. 4) of residual stress B, thevalue of the residual stress is preferably more than or equal to −2000MPa and less than or equal to 1000 MPa. In other words, in the stressdistribution of residual stress B, the absolute value of the compressiveresidual stress is preferably less than or equal to 2000 MPa (i.e., morethan or equal to −2000 MPa and less than 0 MPa), and the absolute valueof the tensile residual stress is preferably less than or equal to 1000MPa (i.e., more than 0 MPa and less than or equal to 1000 MPa). In thiscase, both the chipping resistance and the crater wear resistance tendto be exhibited appropriately.

Moreover, minimum point P3 b is preferably positioned to have a distanceof 0.1 to 40% of the thickness of the α-Al₂O₃ layer 20 from the surface(upper surface) opposite to the substrate. In this case, a damage formof α-Al₂O₃ layer 20 becomes stable to suppress, for example, suddenchipping of the coating film, whereby variation in the life of the toolcan be reduced. For example, when the thickness of α-Al₂O₃ layer 20 is 1to 20 μm, the location of minimum point P3 b is preferably 0.1 to 8 μmfrom the surface opposite to the substrate. Moreover, the value of theresidual stress at minimum point P3 b is preferably −1900 to −100 MPa,is more preferably −1800 to −200 MPa, and is further preferably −1700 to−300 MPa.

(Average Grain Size of Crystal Grains of α-Al₂O₃)

In the present embodiment, the average grain size of the crystal grainsof α-Al₂O₃ is preferably 0.1 μm to 3 μm, and is more preferably 0.2 μmto 2 μm. For example, the average grain size of the crystal grains canbe calculated using the above-described color map. Specifically, first,in the above-described color map, a region having the same color (i.e.,the same plane orientation) and surrounded by different color(s) (i.e.,different plane orientation(s)) is regarded as an individual region ofeach crystal grain. Next, a distance between two points on the outercircumference of each crystal grain is measured, and the longestdistance between two points thereon is regarded as the grain size of thecrystal grain.

(Intermediate Layer)

The coating film preferably further includes one or more intermediatelayers disposed between the substrate and the α-Al₂O₃ layer. Each of theintermediate layers preferably includes a compound that is composed ofat least one element selected from a group consisting of a group 4element, a group 5 element, a group 6 element in a periodic table, Aland Si, and at least one element selected from a group consisting of C,N, B, and O. Examples of the group 4 element in the periodic tableinclude titanium (Ti), zirconium (Zr), hafnium (Hf) and the like.Examples of the group 5 element in the periodic table include vanadium(V), niobium (Nb), tantalum (Ta) and the like. Examples of the group 6element in the periodic table include chromium (Cr), molybdenum (Mo),tungsten (W) and the like. The intermediate layer more preferablyincludes a Ti compound composed of a Ti element and at least one elementselected from a group consisting of C, N, B, and O.

Examples of the compound included in the intermediate layer includesTiCNO, TiAlN, TiAlSiN, TiCrSiN, TiAlCrSiN, AlCrN, AlCrO, AlCrSiN, TiZrN,TiAlMoN, TiAlNbN, TiSiN, AlCrTaN, AlTiVN, TiB₂, TiCrHfN, CrSiWN, TiAICN,TiSiCN, AlZrON, AlCrCN, AlHfN, CrSiBON, TiAlWN, AlCrMoCN, TiAlBN,TiAlCrSiBCNO, ZrN, ZrCN and the like.

The thickness of the intermediate layer is preferably more than or equalto 0.1 μm and less than or equal to 3 and is more preferably more thanor equal to 0.5 μm and less than or equal to 1.5 μm.

(Other Layer(s))

As long as the effects exhibited by the cutting tool according to thepresent embodiment are not compromised, the coating film may furtherinclude other layer(s). The other layer(s) may have a compositiondifferent from or the same as the composition of the α-Al₂O₃ layer orthe intermediate layer. Examples of a compound included in the otherlayer(s) include TiN, TiCN, TiBN, Al₂O₃, and the like. It should benoted that an order of layering the other layer(s) is particularly notlimited. Examples of the other layer(s) includes: an underlying layerprovided between the substrate and the α-Al₂O₃ layer; an outermost layerprovided on the α-Al₂O₃ layer; and the like. The thickness of each ofthe other layer(s) is not particularly limited as long as the effects ofthe present embodiment are not compromised. For example, the thicknessof each of the other layer(s) is more than or equal to 0.1 μm and lessthan or equal to 20 μm.

<<Method for Manufacturing Cutting Tool>>

A method for manufacturing the cutting tool according to the presentembodiment includes:

a step (hereinafter, also referred to as “first step”) of preparing thesubstrate having the rake face;

a step (hereinafter, also referred to as “second step”) of forming thecoating film including the α-Al₂O₃ layer on the rake face of thesubstrate using a chemical vapor deposition method; and

a step (hereinafter, also referred to as “third step”) of performing ablasting process to the α-Al₂O₃ layer at the rake face.

<First Step: Step of Preparing Substrate>

In the first step, the substrate having the rake face is prepared. Forexample, a cemented carbide substrate is prepared as the substrate. Forthe cemented carbide substrate, a commercially available cementedcarbide substrate may be used or a cemented carbide substrate may beproduced using a general powder metallurgy method. In the productionusing the general powder metallurgy method, for example, WC powder, Copowder, and the like are mixed using a ball mill or the like to obtain apowder mixture. This powder mixture is dried and then is formed into apredetermined shape, thereby obtaining a shaped body. Further, bysintering the shaped body, a WC—Co based cemented carbide (sinteredmaterial) is obtained. Next, this sintered material is subjected to apredetermined cutting edge process such as honing, thereby producing asubstrate composed of the WC—Co based cemented carbide. In the firststep, any conventionally known substrate of this type other than theabove-described substrate can be prepared.

<Second Step: Step of Forming Coating Film>

In the second step, the coating film including the α-Al₂O₃ layer isformed on the rake face of the substrate using the chemical vapordeposition method (CVD method).

FIG. 5 is a schematic cross sectional view showing an exemplary chemicalvapor deposition apparatus (CVD apparatus) used to manufacture thecoating film. Hereinafter, the second step will be described withreference to FIG. 5. CVD apparatus 30 includes: a plurality of substratesetting jigs 31 for holding substrates 10; and a reaction container 32that is composed of a heat-resistant alloy steel and that coverssubstrate setting jigs 31. Moreover, a temperature adjusting apparatus33 for controlling a temperature in reaction container 32 is provided tosurround reaction container 32. A gas inlet pipe 35 having a gas inlet34 is provided in reaction container 32. Gas inlet pipe 35 is disposedto extend in the vertical direction and to be rotatable with respect tothe vertical direction in an internal space of reaction container 32 inwhich substrate setting jigs 31 are disposed, and is provided with aplurality of jet holes 36 for jetting a gas into reaction container 32.By using this CVD apparatus 30, each of the layers of the coating film,inclusive of the α-Al₂O₃ layer, can be formed as follows.

First, each of substrates 10 is disposed on a substrate setting jig 31,and a source material gas for α-Al₂O₃ layer 20 is introduced from gasinlet pipe 35 into reaction container 32 while controlling thetemperature and pressure in reaction container 32 to fall withinpredetermined ranges. Accordingly, α-Al₂O₃ layer 20 is formed on therake face of substrate 10. Here, before forming the α-Al₂O₃ layer 20, itis preferable to form the intermediate layer on the surface of substrate10 by introducing a source material gas for the intermediate layer fromgas inlet pipe 35 into reaction container 32. The following describes amethod for forming α-Al₂O₃ layer 20 after forming the intermediate layeron the surface of substrate 10.

Although the source material gas for the intermediate layer is notparticularly limited, examples of the source material gas for theintermediate layer include: a mixed gas of TiCl₄ and N₂; a mixed gas ofTiCl₄, N₂, and CH₃CN; and a mixed gas of TiCl₄, N₂, CO, and CH₄.

The temperature in reaction container 32 during the formation of theintermediate layer is preferably controlled to fall within a range of1000 to 1100° C., and the pressure in reaction container 32 ispreferably controlled to fall within a range of 0.1 to 1013 hPa.Moreover, HCl gas may be introduced together with the above-describedsource material gas. The introduction of HCl gas leads to improveduniformity of the thickness of each layer. It should be noted that it ispreferable to use H₂ as a carrier gas. Moreover, when introducing a gas,it is preferable to rotate gas inlet pipe 35 by a driving unit not shownin the figure. Accordingly, in reaction container 32, each gas can bedistributed uniformly.

Further, the intermediate layer may be formed using a MT (MediumTemperature)-CVD method. The MT-CVD method is a method for forming alayer by maintaining the temperature in reaction container 32 to acomparatively low temperature of 850 to 950° C., unlike a CVD methodperformed at a temperature of 1000 to 1100° C. (hereinafter, alsoreferred to as “HT-CVD method”). Since the MT-CVD method is performed atthe comparatively lower temperature than that in the HT-CVD method,damage to substrate 10 by heating can be reduced. Particularly, when theintermediate layer is a TiCN layer, it is preferable to form theintermediate layer using the MT-CVD method.

Next, α-Al₂O₃ layer 20 is formed on the intermediate layer. As a sourcematerial gas, a mixed gas of AlCl₃, N₂, CO₂, and H₂S is used. On thisoccasion, respective flow rates (L/min) of CO₂ and H₂S are set tosatisfy CO₂/H₂S>2. Accordingly, the α-Al₂O₃ layer is formed. It shouldbe noted that the upper limit value of CO₂/H₂S is not particularlylimited, but is preferably less than or equal to 5 in view of uniformityof the thickness of the layer. Moreover, the present inventors haveconfirmed that flow rates of CO₂ and H₂S are preferably 0.4 to 2.0 L/minand 0.1 to 0.8 L/min, and are most preferably 1 L/min and 0.5 L/min,respectively.

The temperature in reaction container 32 is preferably controlled tofall within a range of 1000 to 1100° C., and the pressure in reactioncontainer 32 is preferably controlled to fall within a range of 0.1 to100 hPa. Moreover, HCl gas may be introduced together with theabove-described source material gas, and H₂ can be used as a carriergas. It should be noted that when introducing the gases, it ispreferable to rotate gas inlet pipe 35 as with the foregoing case.

In order to more improve the effect of the present disclosure, it ispreferable to decrease the temperature in the reaction containercontinuously at a rate (hereinafter, also referred to as “temperaturedecreasing rate”) of 0.1 to 0.3° C./minute for a time (hereinafter, alsoreferred to as “temperature decreasing time”) of more than or equal to30 minutes and less than 90 minutes, preferably more than or equal to 30minutes and less than or equal to 80 minutes, at a final stage of theformation of the α-Al₂O₃ layer. In this way, a tensile residual stressgenerated in the coating film becomes small, with the result that in thesubsequent step of performing a blasting process, a tensile stress canbe reduced and a compressive stress can be introduced more effectively.

It should be noted that an outermost layer may be formed on α-Al₂O₃layer 20 as long as the effects exhibited by the cutting tool accordingto the present embodiment are not compromised. A method for forming theoutermost layer is not particularly limited. Examples thereof include amethod for forming the outermost layer using the CVD method or the like.

Regarding the above-described manufacturing method, a configuration ofeach layer is changed by controlling conditions of the CVD method. Forexample, the composition of each layer is determined by the compositionof the source material gas to be introduced into reaction container 32,and the thickness of each layer is controlled by an execution time (filmformation time). Particularly, in order to decrease a ratio of coarsegrains in α-Al₂O₃ layer 20 and increase crystal grains oriented in the(001) plane, it is important to control a ratio (CO₂/H₂S) of the flowrates of the CO₂ gas and the H₂S gas in the source material gas.

<Third Step: Step of Performing Blasting Process>

In the step of performing the blasting process, the α-Al₂O₃ layer at therake face is subjected to the blasting process. The “blasting process”refers to a process for changing various characteristics of the surfacesuch as orientation and compressive stress by hitting (blasting with) amultiplicity of small spherical bodies (media) such as steel ornonferrous metal (for example, ceramic) against a surface such as therake face at a high speed. In the present embodiment, the blastingprocess is performed onto the rake face to provide a residual stress tothe α-Al₂O₃ layer on the rake face, thus resulting in a differencebetween film residual stress A_(A) and film residual stress B_(A). As aresult, crack progression in the α-Al₂O₃ layer is suppressed, therebyattaining an excellent chipping resistance. The blasting with the mediais not particularly limited as long as film residual stress A_(A) andfilm residual stress B_(A) in the α-Al₂O₃ layer are provided to fallwithin the above-described respective predetermined numerical ranges.The blasting with the media may be performed directly onto the α-Al₂O₃layer or may be performed onto another layer (for example, the outermostlayer) provided on the α-Al₂O₃ layer. The blasting with the media is notparticularly limited as long as the blasting with the media is performedat least onto the rake face. For example, the blasting with the mediamay be performed onto the entire surface of the cutting tool.

Conventionally, the blasting process has been performed to change, intoa compressive stress, a tensile stress remaining mainly in a targetlayer in the coating film. However, it has not been conventionally knownto perform the blasting process so as to bring the film residual stress(film residual stress A_(A)) of the crystal grains oriented in (001) andthe film residual stress (film residual stress B_(A)) of the crystalgrains other than the crystal grains oriented in (001) into the tensileresidual stress and compressive residual stress falling within thepredetermined numerical ranges, respectively. The present inventors havefirst found this.

Moreover, in the conventional blasting process, a blasting pressure ishigh and the coating film is polished at the same time. Accordingly, theconventional blasting process tends to involve breakage of the targetlayer due to the polishing of the coating film. In the presentembodiment, the tensile residual stress generated in the α-Al₂O₃ layerin the second step is smaller than that in the α-Al₂O₃ layer formed inaccordance with the conventional manufacturing method. Accordingly,breakage of the α-Al₂O₃ layer does not take place and a stress is likelyto be introduced into the α-Al₂O₃ layer, with the result that filmresidual stress A_(A) and film residual stress B_(A) can become tensileresidual stress and compressive residual stress falling within thepredetermined numerical ranges, respectively.

Although a mechanism is not known as to a reason why film residualstress A_(A) and film residual stress B_(A) become the tensile residualstress and compressive residual stress falling within the predeterminednumerical ranges respectively by performing the blasting process ontothe α-Al₂O₃ layer, the present inventors consider as follows. It isconsidered that the crystal grains oriented in (001) have a resistanceagainst deformation due to external force because the crystal grainsoriented in the same crystal orientation support one another. On theother hand, it is considered that the crystal grains other than thecrystal grains oriented in (001) have a reduced resistance against thedeformation due to external force because the crystal orientationsthereof are not aligned. It is considered that since the crystal grainsoriented in (001) and the other crystal grains are thus different fromeach other in terms of deformability with respect to external force,there occurs a difference therebetween in terms of residual stressesprovided by the blasting process, with the result that film residualstress A_(A) becomes the tensile residual stress and film residualstress B_(A) becomes the compressive residual stress.

Examples of the material of the media include a steel, a ceramic, analuminum oxide, a zirconium oxide, and the like.

The average grain size of the media is preferably 1 to 300 μm, and ismore preferably 5 to 200 μm, for example.

For the media, a commercially available product may be used. Examplesthereof include ceramic abrasive grains each having a grain size of 90to 125 μm (average grain size of 100 μm) (provided by NICCHU; trademark:WAF120).

A distance (hereinafter, also referred to as “blasting distance”)between a blasting unit for blasting with the media and the surface suchas the rake face is preferably 80 mm to 120 mm, and is more preferably80 mm to 100 mm.

A pressure (hereinafter, also referred to as “blasting pressure”) to beapplied to the media upon blasting is preferably 0.02 MPa to 0.5 MPa,and is more preferably 0.05 MPa to 0.3 MPa.

A process time for the blasting is preferably 5 seconds to 60 seconds,and is more preferably 10 seconds to 30 seconds.

The conditions of the blasting process can be appropriately adjusted inaccordance with the configuration of the coating film.

<Other Step(s)>

In the manufacturing method according to the present embodiment, anadditional step may be performed appropriately in addition to the stepsdescribed above, as long as the effects of the blasting process are notcompromised.

EXAMPLES

While the present invention will be described in detail with referenceto Examples, the present invention is not limited thereto.

<<Production of Cutting Tool>>

<First Step: Step of Preparing Substrate>

As substrates, cemented carbide cutting inserts (shape: CNMG120408N-UX;

provided by Sumitomo Electric Industries HardMetal; JIS B4120 (2013))were prepared each of which was composed of TaC (2.0 mass %), NbC (1.0mass %), Co (10.0 mass %) and WC (remainder) (and included an inevitableimpurity).

<Second Step: Step of Forming Coating Film>

A CVD apparatus was used to form an intermediate layer and an α-Al₂O₃layer in this order on each of the prepared substrates, thereby forminga coating film on a surface of the substrate including a rake face.Moreover, in parts of the samples, the α-Al₂O₃ layer was directly foanedon the substrate without forming the intermediate layer (sample numbers8 and 13). Conditions for forming each layer are described below. At afinal stage of the formation of the α-Al₂O₃ layer, a temperature wasdecreased at a temperature decreasing rate shown in Table 2 for atemperature decreasing time shown in Table 2. A cell with “-” in Table 2means that a corresponding process was not performed. It should be notedthat a value in parenthesis following each gas composition indicates aflow rate (L/min) of each gas. Moreover, the thickness of the α-Al₂O₃layer and the thickness and composition of the intermediate layer areshown in Table 1.

(Intermediate Layer)

Source material gas: TiCl₄ (0.002 L/min), CH₄ (2.0 L/min), CO (0.3L/min), N₂ (6.5 L/min), HCl (1.8 L/min), H₂ (50 L/min)

Pressure: 160 hPa

Temperature: 1000° C.

Film formation time: 45 minutes

(α-Al₂O₃ Layer)

Source material gas: AlCl₃ (3.0 L/min), CO₂ (1.5 L/min), H₂S (2.2L/min), H₂ (40 L/min)

Pressure: 65 hPa

Temperature: 980 to 1000° C.

Temperature decreasing rate: as described in Table 2

Temperature decreasing time: as described in Table 2

Film formation time: 340 minutes

TABLE 1 α-Al₂O₃ Layer Area Ratio of Crystal Area Ratio Grains Orientedin of Other Intermediate Layer Sample (001) Crystal Grains ThicknessThickness Number (%) (%) * (μm) Composition (μm) 1 85 15 4.0 TiCNO 0.6 279 21 6.8 TiCNO 0.8 3 76 24 2.5 TiCNO 1.2 4 73 27 4 TiCNO 1   5 70 309.2 TiCNO 1.6 6 67 33 10.8 TiCNO 1.9 7 62 38 19.2 TiCNO 0.4 8 58 42 14.5— — 11 95 5 1.4 TiCNO 0.2 12 92 8 0.5 TiCNO 1.8 13 41 59 5.2 — — * means“the area ratio of the crystal grains other than the crystal grainsoriented in (001)”

TABLE 2 Conditions of Formation of α-Al₂O₃ Layer in Second StepTemperature Temperature Conditions of Blasting in Decreasing DecreasingThird Step Sample Rate Time Blasting Pressure Number (° C./Minute)(Minute) (MPa) 1 0.25 80 0.3 2 0.25 60 0.3 3 0.2 80 0.25 4 0.2 50 0.2 50.15 80 0.2 6 0.15 50 0.25 7 0.15 30 0.2 8 0.1 80 0.1 11 0.1 10 0.1 120.05 30 0.02 13 — — —

<Third Step: Step of Performing Blasting Process>

Next, the surface, inclusive of the rake face, of the cutting insert(cutting tool) having the coating film formed thereon was subjected to ablasting process under the following conditions. A cell with “−” inTable 2 means that a corresponding process was not performed.

(Blasting Conditions)

Abrasive grain concentration: 5 to 20 wt %

Blasting pressure: as described in Table 2

Blasting time: 5 to 20 seconds

With the above procedure, cutting tools of sample numbers 1 to 8(Examples) and sample numbers 11 to 13 (Comparative Example) wereproduced.

<<Evaluations on Characteristics of Cutting Tool>>

By using cutting tools of sample numbers 1 to 8 and sample numbers 11 to13 produced as described above, characteristics of each of the cuttingtools were evaluated as described below.

<Production of Color Map>

Mirror-polishing was performed to produce a processed surface of theα-Al₂O₃ layer so as to be parallel to the surface of the substrate atthe rake face of the cutting tool having the coating film providedthereon. The produced processed surface was observed at a magnificationof 5000× using an FE-SEM including an EBSD, thereby preparing theabove-described color map for the processed surface with 30 μm×15 μm.The number of color maps prepared on this occasion (the number ofmeasurement visual fields) was 3. For each color map, commerciallyavailable software (trademark: “Orientation Imaging Microscopy Ver 6.2”provided by EDAX) was used to calculate an area ratio of crystal grainsof α-Al₂O₃ oriented in (001) and an area ratio of crystal grains otherthan the crystal grains of α-Al₂O₃ oriented in (001). Results thereofare shown in Table 1. Moreover, as apparent from Table 1, in each colormap, a total of the area ratio of the crystal grains of α-Al₂O₃ orientedin (001) and the area ratio of the crystal grains other than the crystalgrains of α-Al₂O₃ oriented in (001) with respect to the entire area ofthe color map was 100%.

<Measurement of Film Residual Stress by 2θ-sin²ψ Method>

The above-described 2θ-sin²ψ method was employed to measure filmresidual stress A_(A) and film residual stress B_(A) in the α-Al₂O₃layer under the following conditions. Measured film residual stressA_(A) and film residual stress B_(A) are shown in Table 4. In Table 4, aresidual stress indicated by a negative numerical value represents acompressive residual stress, whereas a residual stress indicated by apositive numerical value represents a tensile residual stress.

Apparatus: SmartLab (provided by Rigaku)

X-ray: Cu/Kα/45 kV/200 mA

Counter: D/teX Ultra250 (provided by Rigaku)

Scanning range: 89.9° to 91.4° (inclination method) in the case of filmresidual stress A_(A)

-   -   37.0° to 38.4° (inclination method) in the case of film residual        stress B_(A)

<Measurement of Residual Stress by Constant Penetration Depth Method>

Further, the constant penetration depth method was employed to measureresidual stress A and residual stress B at predetermined depth locationsin the α-Al₂O₃ layer under the following conditions. Table 3 showsresidual stresses A (A_(d10), A_(d40)) and B (B_(d10), B_(d40)) atrepresentative depth locations. In accordance with results ofmeasurement of residual stresses A and B, it was confirmed whether ornot first a region P1 a and second a region P2 a (first b region Plb andsecond b region P2 b) existed in each sample. Moreover, for each ofsamples confirmed to have first b region Plb and second b region P2 b,minimum point P3 b was determined to exist therein (Table 3).

Apparatus: Spring-8 BL16XU

X-ray energy: 10 keV (λ=0.124 nm)

X-ray beam diameter: 0.4 to 1.8 mm (changed depending on penetrationdepth)

Used diffraction plane: (001) plane in the case of residual stress A

-   -   (110) plane in the case of residual stress B

TABLE 3 Constant Penetration Depth Method Residual Stress at DepthResidual Stress at Depth Location of Distance d₁₀ from Location ofDistance d₄₀ from Presence/ Surface Side Surface Side Absence of SampleA_(d10) B_(d10) A_(d40) B_(d40) Minimum Number (MPa) (MPa) (MPa) (MPa)Point P3b 1 −102 −1245 412 213 Present 2 −87 −1140 422 208 Present 3 −60−918 519 330 Present 4 20 −876 719 308 Present 5 50 −812 1090 382Present 6 260 −734 1420 404 Present 7 383 −662 1870 607 Present 8 756−552 1980 660 Present 11 1058 −54 2025 544 Present 12 1800 50 2828 205Absent 13 3133 715 3134 710 Absent

<<Cutting Test>>

(Intermittent Process Test)

Each of the cutting tools of sample numbers 1 to 8 and sample numbers 11to 13 produced as described above was used to measure, under thefollowing cutting conditions, the number of times of making contact witha workpiece until chipping and detachment of the coating film occurredat a cutting edge ridgeline portion. Results thereof are shown in Table4. It can be evaluated that as the number of times of making contact islarger, the cutting tool has a more excellent chipping resistance.

Test Conditions of Intermittent Process

Workpiece: FCD450 grooved material

Cutting speed: 250 m/min

Feed: 0.25 mm/rev

Depth of cut: 2 mm

Cutting fluid: wet type

(Continuous Process Test)

Each of the cutting tools of sample numbers 1 to 8 and sample numbers 11to 13 produced as described above was used to measure, under thefollowing cutting conditions, a cutting time until the depth of a craterwear became 0.1 mm. Results thereof are shown in Table 4. It can beevaluated that as the cutting time is longer, the cutting tool has amore excellent crater wear resistance.

Test Conditions of Continuous Process

Workpiece: SCM435 round bar

Cutting speed: 250 m/min

Feed: 0.25 mm/rev

Depth of cut: 2 mm

Cutting fluid: wet type

TABLE 4 Intermittent Process Test Continuous Number of Times ProcessTest 2θ-sin²ψ Method Making Contact Continuous Film Residual FilmResidual Until Occurrence Process Sample Stress A_(A) Stress B_(A) ofChipping Cutting Time Number (MPa) (MPa) (Number of Times) (Minute) 1 27−978 7218 24.0 2 182 −912 7567 23.8 3 359 −812 7012 24.2 4 589 −692 678921.7 5 987 −483 6080 22.5 6 1267 −406 5463 22.3 7 1588 −312 5698 20.9 81922 −298 5039 21.6 11 2012 −25 720 4.8 12 2099 128 819 3.6 13 3120 712152 4.2

In view of the results of Table 4, each of the cutting tools of samplenumbers 1 to 8 (Examples) attained such an excellent result that thenumber of times of making contact with the workpiece until the chippingand detachment occurred in the intermittent process was more than orequal to 5000. On the other hand, for each of the cutting tools ofsample numbers 11 to 13 (Comparative Examples), the number of times ofmaking contact in the intermittent process was less than 5000. From theabove results, it was found that each of the cutting tools of theExamples (sample numbers 1 to 8) was excellent in chipping resistance.

In view of the results of Table 4, each of the cutting tools of samplenumbers 1 to 8 (Examples) attained such an excellent result that thecutting time in the continuous process was more than or equal to 20minutes. On the other hand, for each of the cutting tools of samplenumbers 11 to 13 (Comparative Examples), the cutting time in thecontinuous process was less than 20 minutes. From the above results, itwas found that each of the cutting tools of the Examples (sample numbers1 to 8) was excellent in crater wear resistance.

Heretofore, the embodiments and examples of the present invention havebeen illustrated, but it has been initially expected to appropriatelycombine configurations of the embodiments and examples.

The embodiments and examples disclosed herein are illustrative andnon-restrictive in any respect. The scope of the present invention isdefined by the terms of the claims, rather than the embodiments andexamples described above, and is intended to include any modificationswithin the scope and meaning equivalent to the terms of the claims.

The above description includes features described below.

(Clause 1)

A method for manufacturing the cutting tool, the method comprising:

a first step of preparing the substrate including the rake face;

a second step of forming the coating film including the α-Al₂O₃ layer onthe rake face of the substrate using a chemical vapor deposition method;and

a third step of performing a blasting process onto the α-Al₂O₃ layer atthe rake face.

(Clause 2)

The method for manufacturing the cutting tool according to clause 1,wherein

the second step includes forming the α-Al₂O₃ layer at a temperature ofmore than or equal to 1000° C. and less than or equal to 1100° C. undera pressure of more than or equal to 0.1 hPa and less than or equal to100 hPa, and

the temperature is decreased continuously at a rate of more than orequal to 0.1° C./minute and less than or equal to 0.3° C./minute for atime of more than or equal to 30 minutes and less than 90 minutes at afinal stage of the formation of the α-Al₂O₃ layer.

REFERENCE SIGNS LIST

1: rake face; 2: flank face; 3: cutting edge ridgeline portion; 10:substrate; 20: α-Al₂O₃ layer; 21: crystal grains oriented in (001); 22:crystal grains other than the crystal grains oriented in (001); 30: CVDapparatus; 31: substrate setting jig; 32: reaction container; 33:temperature adjusting apparatus; 34: gas inlet; 35: gas inlet pipe; 36:through hole; 40: coating film; 50: cutting tool; D1: virtual plane D1;D2: virtual plane D2; P1 a: first a region; P2 a: second a region; P3 a:minimum point; P1 b: first b region; P2 b: second b region; P3 b:minimum point; r1: region r1.

1. A cutting tool comprising: a substrate including a rake face; and acoating film that coats the rake face, wherein the coating film includesan α-Al₂O₃ layer disposed on the substrate, the α-Al₂O₃ layer includescrystal grains of α-Al₂O₃, an area ratio of crystal grains oriented in(001) among the crystal grains is more than or equal to 50% and lessthan or equal to 90% in the α-Al₂O₃ layer at the rake face, and in aresidual stress measurement performed in accordance with a 2θ-sin²ψmethod using X rays, a film residual stress A_(A) determined based on acrystal plane interval of a (001) plane of the α-Al₂O₃ layer at the rakeface is more than 0 MPa and less than or equal to 2000 MPa, and a filmresidual stress B_(A) determined based on a crystal plane interval of a(110) plane of the α-Al₂O₃ layer at the rake face is more than or equalto −1000 MPa and less than 0 MPa.
 2. The cutting tool according to claim1, wherein the α-Al₂O₃ layer has a thickness of more than or equal to 1μm and less than or equal to 20 μm, in a residual stress measurementperformed in accordance with a constant penetration depth method using Xrays at a region r1 interposed between a virtual plane D1 and a virtualplane D2, the virtual plane D1 being located at a distance d₁₀ from asurface of the α-Al₂O₃ layer opposite to the substrate toward thesubstrate side, the distance d₁₀ being 10% of the thickness of theα-Al₂O₃ layer, the virtual plane D2 being located at a distance d₄₀ fromthe surface of the α-Al₂O₃ layer opposite to the substrate toward thesubstrate side, the distance do being 40% of the thickness of theα-Al₂O₃ layer, a residual stress A determined based on the crystal planeinterval of the (001) plane of the α-Al₂O₃ layer at the rake face ismore than or equal to −200 MPa and less than or equal to 2000 MPa, and aresidual stress B determined based on the crystal plane interval of the(110) plane of the α-Al₂O₃ layer at the rake face is more than or equalto −1500 MPa and less than or equal to 700 MPa, and a relationalexpression of A>B is satisfied.
 3. The cutting tool according to claim2, wherein a stress distribution of the residual stress A has a first aregion in which the residual stress A is decreased continuously from thesurface of the α-Al₂O₃ layer opposite to the substrate toward thesubstrate side, and a second a region which is located at the substrateside relative to the first a region and in which the residual stress Ais increased continuously from the surface opposite to the substratetoward the substrate side, and the first a region and the second aregion are continuous to each other via a minimum point of the residualstress A.
 4. The cutting tool according to claim 2, wherein a stressdistribution of the residual stress B has a first b region in which theresidual stress B is decreased continuously from the surface of theα-Al₂O₃ layer opposite to the substrate toward the substrate side, and asecond b region which is located at the substrate side relative to thefirst b region and in which the residual stress B is increasedcontinuously from the surface opposite to the substrate toward thesubstrate side, and the first b region and the second b region arecontinuous to each other via a minimum point of the residual stress B.5. The cutting tool according to claim 1, wherein the coating filmfurther includes one or more intermediate layers disposed between thesubstrate and the α-Al₂O₃ layer, and each of the intermediate layersincludes a compound that is composed of at least one element selectedfrom a group consisting of a group 4 element, a group 5 element, a group6 element in a periodic table, Al and Si, and at least one elementselected from a group consisting of C, N, B, and O.